The present invention generally relates to extruding machines and methods for extruding material that has an abrasive characteristic.
As used herein, "extrude" means to force, press, push out, shape, or the like a material by forcing the same through a die. An "extruder" or an "extruding machine" means an apparatus for performing the act of extruding. Moreover, "extrusion" means an article or material produced by the use of an extruder, and a "fresh extrusion" or "green ware" means an extrusion that has just been extruded. "Extrusion material" means the ingredients being extruded. "Fluid" is used in its generic sense to mean either a liquid or a gas or other material that has fluid-like properties, e.g. capable of flowing.
A conventional extruder is exemplified by one sold under model type YX-8 by Plymouth Locomotive Works, Inc., Plymouth, Ohio. Such extruder includes a dual shaft plug mill in which the extrusion material is mixed and from which the extrusion material is delivered via a seal to a vacuum chamber where air is removed from the extrusion material to increase its uniformity, to reduce air bubbles in the extrusion, and the like. The auger, auger housing, and extrusion material therein provide a seal at the extrusion material outlet from the vacuum chamber to prevent escape of the vacuum therefrom. The seal at the entrance to the vacuum chamber is formed by a hollow tapered, e.g. truncated conical, sealing die and an oppositely tapered sealing core between which is defined a tapered volume that has a wide entrance into which extrusion material is driven from the pug mill by a sealing auger and a narrow exit through which the extrusion material is delivered to the entrance of the vacuum chamber. The extrusion material effectively is compressed in such tapered volume and cooperates with the tapered sealing die and core to provide the seal function blocking escape of vacuum from the vacuum chamber.
It has been found that relatively abrasive extrusion material sometimes has difficulty passing through such seal to the extent that a seizure is encountered which may damage the extruder. Accordingly, there is a need to facilitate the delivery of abrasive extrusion material into the vacuum chamber of an extruder while maintaining an effective seal at the entrance to such chamber.
In the past, to keep the extruder and extrusion material warm steam jackets were placed about one or more extruder components so that heat from steam in such jackets would provide warmth. However, such heating system was relatively inefficient since the outside of the steam jacket was exposed to ambient conditions and, therefore, itself lost heat to the ambient environment.